Wellington’s Engineers: Military Engineering on the Peninsular War 1808-1814 (35 page)
Read Wellington’s Engineers: Military Engineering on the Peninsular War 1808-1814 Online
Authors: Mark S. Thomson
Tags: #Non-Fiction, #History, #Military, #Napoleonic Wars, #Spain, #Portugal, #Engineering
Appendix 4
Military Bridging
The Iberian Peninsula was a hostile environment for Napoleonic armies. Much of the country was covered with mountains, making traversing it difficult, if not impossible. In between the mountain ranges flowed wide and fast-moving rivers that could only be crossed by bridges or boats. Rain or snow in the mountains could raise the level of rivers by several feet overnight and sweep away any crossing-points. These rivers intersected the country and without a crossing-point an army could be faced with long marches to get from one side to the other. Where there were no mountains or rivers, there were plains; barren in the winter and baking hot in the summer. Roads were rarely better than rough tracks. The royal roads between major towns might be fully cobbled but these were very rare. The best normal road might have two lines of paving stones for wagon wheels but did not allow for passing. Most roads would be hard-packed earth, passable in summer but muddy in the winter. In all cases, maintenance was minimal. It was the geography as much as anything else that defeated Napoleon’s troops in Spain.
For nearly 2,000 years the Spanish had dealt with the major rivers by building strong bridges and knowing every crossing-point at the different seasons of the year. Several bridges built by the Romans still stood proud, such as those at Almaraz, Alcantara and Salamanca. Every campaign during the war relied to some extent on controlling, constructing or destroying bridges.
One of the Allies’ first tasks in 1808 was to establish crossing-points on the river Tagus in Portugal to allow rapid movement between the north and south of the country. Initially this was achieved through floating bridges (ferries) but later they were replaced by pontoon bridges. The boat bridges at Abrantes, Punhete and Villa Velha remained key crossing-points in all operations for the remainder of the war. These were carefully guarded and taken down whenever there was a threat from the enemy. Keeping these in place required constant attention and maintenance, as they were large structures. Lieutenant Harry Jones RE described the boat bridge at Villa Velha when he passed in December 1812. The breadth of river was 140 paces (105m); distance of boat to boat (centre), ten paces (8m). It was made up of twelve large and two smaller boats, each having two anchors. To ensure there was no interruption in its availability, ten boats were kept in reserve.
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He similarly described the bridge at Punhete that was made of short, stout pontoons. The length of the bridge was 160 yards (150m), made up of twenty-one pontoons. The distance from centre to centre of the boats was eight yards (8m). These pontoons only needed one anchor, as the river was less rapid. Each of these had a permanent engineering presence and a guard.
As well as strategic crossing-points, bridging featured in operational campaigns. Moore’s retreat to Corunna in 1808/9 included the destruction of several bridges to delay the advance of the French. The destruction of the bridge at Castro Gonzalo (Benevente) led the repulse of the pursuing French cavalry and to a respite for the Allies. Several engineer officers were involved in destroying bridges and one, Lieutenant Davy, lost his life by misjudging his fuse. There was widespread concern in the Royal Engineers about the limited success in blowing-up bridges.
Wellington’s first success in 1809 was when he ejected Marshal Soult from the Portuguese city of Oporto. The French had destroyed the bridge there and to pursue them required a boat bridge to be rapidly built to allow the bulk of the pursuing Allied troops to cross. This was done using the numerous local boats that were employed in the wine trade. The 1809 Talavera campaign relied on control of bridges further up the Tagus at Alcantara and Almaraz, and by the end of the year both of these bridges had been made impassable and the nearest intact crossing-point was at Arzobispo, which is much nearer to Madrid than Lisbon. The French constructed a boat bridge at Almaraz but this was not possible at Alcantara due to the steepness of the valley and the speed of the river. The Royal Staff Corps built an additional temporary bridge over the river Tietar for the passage of Wellington’s army. The river was about 150 feet (50m) wide, which contained a deep channel about 70 feet (20m) wide. There were no pontoons or boats available in the vicinity:
The only material at hand was the timber from a large inn at about half a mile from the place … which was unroofed … a party of 500 men [taken from the line regiments] with saws and axes was sent to a distance of three miles to procure young pines to make [twenty] stakes.
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The main roof beams from the inn, 20 feet long and two feet square, were floated in the deep channel. Piles were then driven into the shallow part of the river using ‘large wooden mallets made on the spot’. The rafters and flooring from the inn provided enough decking to complete the bridge the whole held in place with ropes. This bridge was constructed in one day.
Whilst the major campaigns of 1809 to 1811 focussed on access to the major
strategic
bridges over the Tagus, smaller bridges were also used and discarded in the various
operational
campaigns. Wellington destroyed several bridges as the French army advanced through Spain into Portugal in 1810 as he retired into the Lines of Torres Vedras. Masséna did the same when he retreated the following March. As Wellington pursued him north he was faced with a number of obstacles. First the bridge over the Alva at Ponte de Murcella needed to be repaired. The Royal Staff Corps built a floating bridge as there was insufficient material to construct a full bridge. A few weeks later, Wellington needed a further crossing-point over the Coa near Almeida, Masséna having also destroyed this bridge. The Royal Staff corps, once again, made the bridge usable, using locally-sourced wood to fill the gap.
1811 saw major problems as the Allies now began to take the offensive. The focus of the operations moved further south and the crossing-points over the Guadiana now became more important, the only two major ones being under the castle at Badajoz and at Merida. The Allied sieges of Badajoz were seriously impeded due to the lack of a pontoon train and the difficulty in keeping the temporary bridges made from trestles, wine casks and pontoons in place in the changeable weather. Further north, when Wellington was threatened by a superior French army at the Battle of Fuentes del Oñoro, he arranged to have a temporary bridge built across the river Coa in case he needed to retreat.
The bridge over the Coa at Fuentes d’ Oñoro
.
January 1812 saw a trestle bridge built across the river Agueda by the Royal Staff Corps to enable Allied troops to approach and besiege Ciudad Rodrigo. Wellington had recognised that a proper bridge was essential and that it would have to be very strong to survive the torrents of water that flowed during the winter. There was no way a pontoon bridge would survive these conditions so the decision was made to construct a trestle bridge. Large amounts of timber were required as the river was about 400 feet (125m) wide. Henry Sturgeon RSC was ordered to prepare the bridge and work started in October 1811. The foot of each trestle was tapered and weigh down with rocks to resist the water flow. This bridge was constructed in appalling winter weather and remained in place throughout the siege. It was then dismantled and stored in Almeida in case it was needed again.
As in the previous year, the third siege of the fortress of Badajoz was hampered by the problems in keeping a pontoon bridge across the river Guadiana. 1812 also saw the Allied lines of communication significantly improved through an innovative repair to Trajan’s Roman bridge at Alcantara. At the same time, Wellington ordered a raid to destroy the French pontoon bridge at Almaraz. Combined, these two actions meant that Wellington could manoeuvre his troops much faster than the French. Following the siege at Burgos, the engineering services played a major role in slowing the French pursuit by destroying bridges
1813 was the first time a pontoon train travelled with the army. It was used a number of times during the Allied advance that led to the successful battle at Vitoria. Later in the year a range of methods were used to cross the rivers Bidassoa, Nivelle and Nive around the French border. 1814 started with the daring crossing of the fast-flowing and tidal river Adour where the wide river was bridged using local boats held in place with five massive cables. Around twenty-five were used with several being held in reserve.
Wellington had to use pontoons to cross numerous rivers as he pushed the retreating French army further east. He was close to disaster at Toulouse when the pontoon bridge over the river Garonne was swept, away leaving part of the Allied army stranded on the wrong side of the river for three days.
The quick summary above shows that river crossing was an essential component of Wellington’s strategy throughout the war. Whilst these were the key events, officers from the Royal Engineers and Royal Staff Corps along with their Portuguese, Spanish and Hanoverian counterparts laboured throughout the war to keep a myriad of smaller river crossings operational.
The bridge over the Adour, from Douglas
.
As discussed earlier, there were three British engineering units present, the Royal Engineers, the Royal Military Artificers (the Royal Sappers and Miners from 1812) and the Royal Staff Corps. Theoretically there was a distinction, in that the role of the Royal Engineers was for static defences i.e. the attack and defence of fortresses whilst mobile work was the responsibility of the Royal Staff Corps i.e. field works and bridging. There is still a debate going on about bridging, as the perceived view is that it was primarily done by the RSC. My research indicates that the Royal Engineers did most bridging work. There is a difference in that the Royal Engineers tending to do most destruction whilst the Royal Staff Corps were more involved in construction. What is apparent is that the officers from the different corps did share information and experience for the benefit of all. The
picture
of the bridge at Ponte de Murcella comes from Douglas’ book on military bridging. Identical pictures are in the contemporary notebooks of Engineer and Staff Corps officers (Burgoyne, Scott and West).
What all the engineer officers faced was a lack of resources, both in men and materials. This meant that river crossings often had to be made with whatever material was available. At its simplest this could be preparing the banks and bed of a river for fording. For smaller rivers and smaller loads, pontoons or boats could be rowed across, sometimes with lines to keep them in place.
The real challenge came when large bodies of troops or heavy loads needed to cross big rivers. Here the nature of the river determined the bridging methods that could be used. Flying bridges, trestles, local boats, wine casks and pontoons were all used at different times. The most frequent method was probably the repair of an existing bridge. More often than not, temporary repairs were carried out using locally-sourced wood. There are many examples where the material obtained either from nearby woods or by dismantling buildings. The two most impressive examples of this during the war were the repair to the stone bridge at Alcantara in 1812 and the crossing of the Adour in 1814. The repairs to the bridge at Alcantara (and also Almaraz) were designed by Henry Sturgeon and Alexander Todd of the Royal Staff Corps. The design is described by Andrew Leith-Hay:
The arch destroyed was of so extensive a span, and the parapet of the bridge so great a height from the bed of the river, that no repair by using timber was practicable; the gap to be passed over being ninety feet wide, and the height of the bridge, one hundred and eighty from the bed of the river … The work was commenced by placing two beams on supporters four feet high and ninety feet asunder. These were secured to the side and end walls of the building by braces and tackles, to prevent their approximating by the straining of the ropes. Eighteen cables were then stretched round them, extending from end to end; eight pieces of timber, six inches square, at equal distances, were placed upon the ropes, with notches, one foot asunder, cut on their surface to secure them; these notches were seared with hot irons to prevent the ropes from chafing. The cables were then lashed to the beams; they were netted together by rope-yarn, and chains of sleepers were bolted and laid on the network, and secured to the two beams originally placed at the extremities of the work. Planks were cut and prepared for being laid across, bored at the ends so as receive a line destined to secure them to the sleepers and to each other … The next point was to prepare the edge of the fractured part of the bridge, and to cut channels in the masonry for the reception of the purchases. When arrived on the spot, four strong ropes were stretched from side to side, as conductors, for passing the cable-bridge across, the beam on the south side having been previously sunk into the masonry; the whole was then stretched by windlass erected on the opposite pier, by which means it was so tightly drawn as to prevent any great sinking, or the vibration which might render it insecure and dangerous, even when heavy weights were passed over.
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